The present invention relates to a plasma processing apparatus and a plasma processing method; and, more particularly, it relates to a plasma processing apparatus and a plasma processing method with which it is possible to suppress the occurrence of obstacles caused by reaction products.
Materials to be etched, which are used in the field of semiconductor device production, can include volatile materials, such as Si, Al and SiO2, for example, for a DRAM (Dynamic Random Access Memory) or logic circuit IC. Further, non-volatile materials, such as Fe, have been adopted for a FRAM (Ferroelectric Random Access Memory) or a MRAM (Magnetic Random Access Memory).
The non-volatile materials are difficult to etch since the melting point of the reaction products that are formed during etching is high. Further, since the vapor pressure of the reaction products after etching is low and the deposition coefficient to the inner walls of the vacuum vessels (vacuum processing chamber) is high, the inner walls of the vacuum vessels tend to become covered with deposits of the reaction products, even after processing only a small amount of samples (several to several hundreds of sheets). Further, when they have peeled and fallen, the deposits form obstacles.
When the reaction products are deposited, the coupling state between induction antennas and plasmas in the reactor changes so as to vary, with time, the etching rate or the uniformness thereof, as well as the vertical etching property, the deposition states of the reaction products on the etching side wall, etc.
Since examples of the non-volatile materials include Fe, NiFe, PtMn, and IrMn as ferromagnetic or anti-ferromagnetic materials used for MRMA or magnetic heads, as well as Pt, Ir, Au, Ta, and Ru as noble metal materials used for capacitor portions or gate portions in a DRAM, capacitor portions in a MRAM and TMR (Tunneling Magneto Resistive) elements in a MRAM. In addition, they can also include Al2O3, HfO3, and Ta2O3 as highly dielectric materials, and PZT (Lead Titanate Zirconate), BST (Barium Strontium Titanate) and SBT (Strontium Bismuth tantalate).
Further, also in the field of semiconductor device production, a technique of forming Si, SiO2 or SiN films by a plasma CVD method has frequently been adopted in the steps for production of semiconductor devices. According to this technique, a polymerizable gas, such as monosilane, is injected into plasmas to form films on a wafer. In this process, a great amount of polymer films are deposited on the inner wall of a reactor, other than on the wafers, thereby to inhibit the mass production stability. That is, when polymer film is deposited to an excessive thickness on the inner wall of the reactor, the polymer film peels and falls from the surface of the inner wall and adheres on the wafer as obstacles in the same manner as described previously. Accordingly, it is necessary to conduct plasma cleaning by using a violent special gas, such as NF3, or to conduct manual cleaning after opening the reactor.
In addition, in the field of semiconductor device production, a SiO2 plasma dry etching step is used frequently. In the type of etching, a fluoro carbon, such as C4F8, C5F8, CO, CF4 and CHF3, is used as an etching gas. Reaction products that are formed by reaction of such gas in the plasmas contain a great amount of free radicals, such as C, CF, C2F2; and, when the free radicals are deposited on the inner wall of the reactor, they cause obstacles to be created, as in the case described previously. Further, when the free radicals are evaporated again in the plasmas, they change the chemical composition of the plasmas so as to cause the wafer etching rate to vary with time.
An induction type plasma processing apparatus, in which coiled antennas are disposed on the outer circumference of a vacuum vessel, or a plasma processing apparatus in which a microwaves are introduced into the vacuum vessel, have been known as existent plasma processing apparatuses. In any of the processing apparatuses described above, since countermeasures for the preventing formation of deposited matter on the inner wall of the vacuum vessel, in the case of etching a non-volatile material, are not completely effective, a manual cleaning operation, which involves opening the vacuum vessel to the atmosphere, needs to be conducted repeatedly. Since manual cleaning requires as much as 6 to 12 hours from the start of the cleaning to the start of the processing for the next sample, this lowers the operation efficiency of the apparatus.
For example, Japanese Patent Laid-open Nos. 10-275694, 11-74098 and 2000-323298 disclose a plasma processing apparatus in which plasmas are generated by an induction method in a processing vessel, a Faraday shield is formed between induction antennas disposed on the outer circumference of the vacuum vessel and the plasmas, and an RF power source is connected to the Faraday shield to supply electric power, thereby reducing the deposition of reaction products on the inner wall of the vacuum vessel, or enabling cleaning of the inner wall of the vacuum vessel.
This apparatus is effective for the portions of the vacuum vessel that are formed of a non-conductive material, such as ceramics or quartzes and the portions that effective electric fields due to the Faraday shield can reach. However, the apparatus is not effective for other portions that are formed of non-conductive materials or conductive materials.
As has been described above, when reaction products are deposited excessively on the inner wall of the vacuum vessel, deposited films tend to peel and fall from the surface of the inner wall and adhere as obstacles on the wafer. Further, in the plasma processing apparatus using induction antennas, the coupling state between the induction antennas and the plasmas in the reaction vessel is changed so as to vary the etching rate and the uniformness thereof, as well as the vertical etching property, and the deposition state of the reaction products on the etching side wall. Further, when the inner wall of the vacuum vessel is cleaned, since it takes much time until the start of the processing for the next sample, the operation efficiency of the apparatus is lowered. Further, in the plasma processing apparatus in which it is intended to decrease the adhesion of reaction products on the inner wall of the vacuum vessel, or to enable cleaning of the inner wall of the vacuum vessel by providing a Faraday shield between the induction antennas disposed on the outer circumference of the vacuum vessel and the plasmas and connecting the RF power source to the Faraday shield to supply electric power thereto, the range of the desired effect is limited.